A power company generates power by a plurality of power generating units such as nuclear power plant, natural gas thermal power plant, oil thermal power plant, coal thermal power plant, hydraulic power plant, solar power plant, wind power plant, biomass power plant, geothermal power plant, wave power plant, ocean thermal energy conversion power plant, tidal power plant, and tidal current power plant. The power generated by the above power generating units is classified broadly into two types: green power generated by a method emitting a small amount of carbon dioxide; and non-green power generated by a method emitting a great amount of carbon dioxide. The two types of power is mixed and supplied to customers.
It is expected that customers will be more conscious about the reduction in the amount of carbon dioxide emission, and customers are encouraged to use green power in their energy-consuming appliances. However, the supply of green power is limited, and thus it is difficult to completely satisfy the power demand of customer appliances only with green power.
Further, in the future, demand response will be introduced to control the power consumption of each appliance based on the information of power supplied by a power system. In order to implement this demand response, it is necessary to increase the acceptability of power consumers by carefully controlling the operation mode etc. of each appliance, which is because the acceptability of power consumers may possibly be reduced if the power supplied to each appliance is merely turned ON/OFF.